Adenotonsillectomy (AT) is one of the most common surgical procedures performed in children, with more than 500,000 operations performed annually in the US. A large proportion of these are performed in children with primary snoring, or mild sleep-disordered breathing (MSDB) rather than in children with frank obstructive sleep apnea. Although AT has been shown to improve behaviour and quality of life in school-aged children with sleep apnea, the role of this common surgery in children with MSDB is not known, resulting in large practice and geographic variation in its use. Considering the morbidity and health care costs of AT, it is crucial to determine the impact of the surgery on outcomes of value to patients and the healthcare system. We propose to take advantage of a successful collaboration of leaders in sleep medicine, otolaryngology, neuropsychology and clinical trials to conduct a randomized clinical trial of AT for MSDB. The overall hypothesis of this proposal is that children with MSDB benefit from AT as defined by improved behaviour and attention (primary outcomes) and decreased health care utilization. Using a single-blinded, randomized design, we aim to recruit 460 children (50% minority), aged 3-9 years, with polysomnographically-confirmed MSDB from 5 leading pediatric centers. Participants will be randomized to early AT or watchful waiting with supportive care, and undergo standardized evaluations of sleep, behavior, attention, quality of life, and health care utilization at baseline and 12 months. Body habitus, urinary cotinine levels, actigraphy, family functioning, atopy and socioeconomic status will be assessed to identify potential moderating influences. This rigorous design and comprehensive study will resolve existing uncertainties on initial management approaches for pediatric MSDB by addressing several critical issues: a) assess outcomes of importance to children and their families, particularly the patient- reported outcomes of behavior, quality of life, and sleep disturbances); b) examine differences in treatment responses among children who are at increased risk for MSDB, such as pre-school children, minorities, and children with asthma or obesity; c) evaluate health care utilization as a unique and timely outcome; d) assess moderating influences of second hand smoke, insufficient sleep, socioeconomic status and family functioning. Study results will provide evidence on whether children with MSDB benefit from surgery and will identify subgroups who are most likely to benefit, thus informing future management approaches of this common pediatric condition and helping to direct resources to those children most likely to benefit.